Now that they're recommended indoors again, let's take a closer look at the filter in an FFP2 mask to understand how it protects us from microscopic invaders.Masks, like a wall, prevent the passage of viruses and bacteria.The authors of this photograph, distinguished in the Fotciencia contest in the special modality 'Science against covid' -Alberto Martín Pérez, Raquel Álvaro Bruna and Eduardo Gil Santos-, wanted to see closely why it is so difficult for them to go through the filter of an FFP2 mask, because, although the masks "have no direct relationship with our work (our research is focused on developing new devices and techniques to be able to measure physical properties and detect objects on the micro and nanoscopic scale, with special interest in particles biological, such as cells, bacteria or viruses), as good scientists, we are very curious", admits Martín.The FFP2 mask was of special interest to them, researchers from the Institute of Micro and Nanotechnology of the Higher Council for Scientific Research (CSIC), because they used the Proveil/Bioinicia mask, made with nanofibers whose synthesis process was developed by researchers from another center of the CSIC."Since our specialty is nanotechnology, we were very interested in seeing what those nanofibers looked like."And they dared to look at them in the latest generation scanning electron microscope (SEM) of the CSIC Institute of Micro and Nanotechnology where they work.The image shows, "in dark blue, the nanometric-thick fibers (the part that can only be seen with SEM) and in light blue, the largest network (the one that would be seen in the optical microscope and that turns out to be useful as a support for nanometric-sized fibers) –explains Martín–. The black parts are the holes in the framework through which air can pass".It is easy to understand that "they work just like a kitchen strainer, the only difficult thing is that this happens on a scale that is beyond the reach of our eyes", simplifies the main author of this image.When we exhale, we expel a mixture of gases that contain microscopic aerosols in suspension.If the person is infected with any respiratory virus (such as SARS-CoV-2 or the flu virus), those aerosols will contain the virus and can infect other people if they breathe them in."By using this 'strainer' that are the masks, we get those drops with the capacity to infect more people to be trapped, while the air can pass freely so that we breathe in and out without problem," he indicates.But that 'strainer' effect has other aids.Javier Ballester, from the University of Zaragoza, explains that "masks and HEPA filters have spaces between fibers that are much larger than the aerosols they retain. The particles, especially the smallest ones (below the micron and the tenth of a micron), they pass through these gaps, but they are retained on the fibers because other very different effects act (inertial impact, electrostatic forces, Brownian diffusion) that make the aerosols go towards the fibers and are retained".While the light microscope allows us to explore the microscopic world, the scanning electron microscope (SEM) is a window to explore the nanoscale.Martín explains that "the optical microscope forms images by shedding light on the sample and collecting the light that it reflects. It allows us to see objects of sizes up to approximately 1 micrometer (that is, a thousand times smaller than a millimeter)".On the contrary, "the SEM forms images by throwing electrons on the sample and collecting the electrons that it emits".It has the advantage that "it allows us to see objects down to a size (approximately) of 1 nanometer (that is, a million times smaller than a millimeter)".However, the SEM "only allows us to see black and white images (the image presented is colorized by computer)".Before looking at the filter of these masks in the SEM, Alberto Martín says that he took "a quick look at them in an optical microscope, to get an idea of ​​what was waiting for us and I found something very curious: it seemed that the FFP2 masks had a mesh with holes much larger than surgical masks (the holes in the mesh of surgical masks are less than or equal to 1 micrometer, while the holes we observed in the filter of the FFP2 mask were several tens of micrometers). micrometers).If what we saw in the optical microscope was true, it would mean that the filtering capacity of FFP2 masks is much lower than that of surgical masks.And not only that, but they would have a filtering capacity similar to that of surgical masks. cloth masks (which is practically nil)".However, when they saw the sample in the SEM, they verified that it was not what it seemed: what in the optical microscope was shown as an empty space, in the SEM it appeared as a space filled with fibers a few hundred nanometers thick.Alberto Martín Pérez, who was in charge of editing the image and preparing the explanatory text, is a Ph. , was a postdoctoral researcher at the Institute of Micro and Nanotechnology).At that CSIC center, Eduardo Gil Santos, Ph.D. in Physics, is a Ramón y Cajal researcher;and Raquel Álvaro Bruna, an industrial technical engineer, is a laboratory and scanning electron microscope technician.She is in charge of managing and maintaining the scanning electron microscope (SEM).She is a barrier against microscopic invaders, they humorously point out that "the great problem that science is facing now is to ensure that the rubber bands of the masks do not bother the ears."In addition to FFP2 masks from very close up, chemical gardens, olive leaves, myxomycetes, magnetic fields, sunflowers, stars and integrated circuits starred in the images selected in the 18th edition of the Fotciencia contest.This initiative of the Spanish Foundation for Science and Technology (Fecyt) and the Higher Council for Scientific Research (CSIC) with the collaboration of the Jesús Serra Foundation, dedicates specific modalities to microphotography, sustainable agriculture, food and The education.Impressive images to arouse curiosity and end up discovering a new angle of science.-Go to the Third Millennium supplementSign up and receive the science newsletter in your email every week© HERALDO DE ARAGON EDITORA, SLU Telephone 976 765 000 / - Pº.Independencia, 29, 50001 Zaragoza - CIF: B99288763 - Registered in the Mercantile Registry of Zaragoza in Volume 3796, Book 0, Folio 177, Section 8, Sheet Z-50564 Any reproduction without written permission from the company is prohibited for the purposes of the article 32.1, second paragraph, of the Intellectual Property Law